04 RA41204EN20GLA0 Radio Propagation Fundamentals v03

Radio Propagation Fundamentals

LTE RPESS Radio Propagation Fundamentals

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Nokia Siemens Networks Academy Legal notice Intellectual Property Rights All copyrights copyrights and intellectual intellectual property property rights for Nokia Nokia Siemens Networks Networks training documentation, documentation, product documentation and slide presentation material, all of which are forthwith known as Nokia Siemens Networks training material, are the exclusive property of Nokia Siemens Networks. Nokia Siemens Networks owns the rights to copying, modification, translation, adaptation or derivatives including any improvements or developments. Nokia Siemens Networks has the sole right to copy, distribute, amend, modify, develop, license, sublicense, sublicense, sell, transfer and assign the N okia Siemens Networks training material. Individuals Individuals can use the Nokia Siemens Networks training material for their own personal self-development only, those same individuals cannot subsequently pass on that same Intellectual Property to others without the prior written agreement of Nokia Siemens Networks. The Nokia Siemens Networks training material cannot be used outside of an agreed Nokia Siemens Networks training session for development development of groups without the prior written agreement of Nokia Siemens Networks.

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© No Nokia Siemens Networks

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Module Objectives After completing this module, the participant should be able to:

• Understand basic radio propagation mechanisms • Understand fading phenomena • Calculate free space loss

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Module Contents Propagation mechanisms Multipath And Fading Propagation Slope And Different Environments

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Module Contents Propagation mechanisms

• • • • •

Basics: deciBel (dB) Radio channel Reflections Diffractions Scattering

Multipath And Fading Propagation Slope And Different Environments

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deciBel (dB) – Definition Power

 P  dB = 10 log   P 0 

P(dB)

[ P lin. ] = 10

10

Voltages

 E  dB = 20 log   E 0 

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E (dB)

[ E lin. ] = 10

20

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deciBel (dB) – Conversion Calculations in dB (deciBel) • Logarithmic scale always with respect to a reference • dBW = dB above Watt dB above mWatt • dBm = = dB above isotropic • dBi = dB above dipole • dBd dB above µV/m • dBµV/m = Rule-of-thumb: factor 2 • +3dB = factor 5 • +7 dB = factor 10 • +10 dB = factor 1/2 • -3dB = • -7 dB = factor 1/5 • -10 dB = factor 1/10

-30 dBm = 1 µW -20 dBm = 10 µW -10 dBm = 100 µW -7 dBm = 200 µW -3 dBm = 500 µW

0 dBm = 1 mW +3 dBm = 2 mW +7 dBm = 5 mW +10 dBm = 10 mW +13 dBm = 20 mW +20 dBm = 100mW +30 dBm = 1 W +40 dBm = 10W +50 dBm = 100W

LTE: UE: max. 23 dBm eNB: typ. 43 / 46 dBm 7


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Radio Channel – Main Characteristics Linear

• In field strength Reciprocal

Remember:

• UL & DL channel same (if in same frequency)

Multipath Effects

Dispersive

→

Normal / Extended CP

• In time (echo, multipath propagation) • In spectrum (wideband channel)

direct path a m p l i t u d e

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echoes

delay time

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Propagation Mechanisms – (1/2) Free-space propagation

• Signal strength decreases exponentially with distance

D

Reflection Specular reflection phase f

 

polarisation

material dependant

amplitude A

a*A (a < 1) - f

phase shift

specular reflection

Diffuse reflection amplitude A phase f phase polarisation 9


 

a *A (a < 1) random

diffuse reflection

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Propagation Mechanisms – (2/2) Absorption • Heavy amplitude attenuation • Material dependant phase shifts

A

A - 5..30 dB

• Depolarisation

Diffraction • Wedge - model • Knife edge • Multiple knife edges

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Scattering – Macrocell Scattering local to mobile

• Causes fading • Small delay and angle spreads • Doppler spread causes time varying

Scattering to base station

effects Scattering local to base station

• No additional Doppler spread • Small delay spread • Large angle spread

Scattering to mobile

Remote scattering

• • • •

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Independent path fading No additional Doppler spread Large delay spread Large angle spread


Remote scattering

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Scattering – Microcell Many local scatterers: Large angle spread Low delay spread Medium or high Doppler spread

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Module Contents Reflections, Diffractions And Scattering Multipath and Fading

• • • •

Delay – Time dispersion Angle – Angular Spread Frequency – Doppler Spread Fading – Slow & Fast

Propagation Slope And Different Environments

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Multipath propagation Radio signal propagates from A to B over multiple paths using different propagation mechanisms

• Multipath Propagation • Received signal is a sum of multipath signals Different radio paths have different properties

• Distance  Delay/Time • Direction  Angle • Direction & Receiver/Transmitter Movement

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

Frequency

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Delay – Time dispersion Multipath delays due to multipath propagation

• 1 µs ≅ 300 m path difference LTE  CP to mitigate multipath effects

• CP (normal or extended) covers some 1.4 km or 20 km delay respectively • Standardized delay profiles in 3GPP specs: – – – –

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TU3

typical urban at 3 km/h (pedestrians)

TU50

typical urban at 50 km/h (cars)

HT100

hilly terrain (road vehicles, 100 km/h)

RA250

rural area (highways, up to 250 km/h)


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Delay Spread

Multipath propagation

1.

P

Channel impulse response 1.

=>

2. 3. 4.

2.

t

f1

4th floor

f1

3rd floor

f1

2nd floor

f1

1st floor

BTS

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Delayed components in DAS (Distributed antenna systems) 

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Delay Spread

Typical values

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Environment

Delay Spread (µs)

Macrocellular, urban

0.5-3

Macrocellular, suburban Macrocellular, rural

0.5

Macrocellular, HT

3-10

Microcellular

< 0.1

Indoor

0.01...0.1

0.1-0.2

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Angle – Angular Spread Angular spread arises due to multipath, both from local scatterers near the mobile and near the base station and remote scatterers Angular spread is a function of base station location, distance and environment Angular Spread has an effect mainly on the performance of diversity reception and adaptive antennas

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Angular Spread Macrocell Antenna

Macrocellular Environment = Macrocell Coverage Area

Microcell Antenna Microcellular Environment = Microcell Coverage Area

5 - 10 degrees in macrocellular environment >> 10 degrees in microcellular environment < 360 degrees in indoor environment

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Frequency – Doppler Spread With a moving transmitter or receiver, the frequency observed by the receiver will change (Doppler effect)

• Rise if the distance on the radio path is decreasing • Fall if the distance in the radio path is increasing The difference between the highest and the lowest frequency shift is called Doppler spread

f d =

v: c: f:

20

v

λ

=

v c f

Speed of receiver (m/s) Speed of light (3*108 m/s) Frequency (Hz)


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Fading Fading describes the variation of the total pathloss ( signal level) when receiver/transmitter moves in the cell coverage area Fading is commonly categorised to two categories based on the phenomena causing it

• Slow fading: Caused by shadowing because of obstacles • Fast fading: Caused by multipath propagation Time-selective fading: Short delay + Doppler Frequency-selective fading: Long delay Space-selective fading: Large angle

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Fading – Slow & Fast

power

Rayleigh fading

+20 dB

lognormal fading

mean value

- 20 dB

2 sec

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4 sec

6 sec

time

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Slow Fading – Gaussian Distribution Measurement campaigns have shown that slow fading follows Gaussian distribution

• Received signal strength in dB scale (e.g. dBm, dBW) Gaussian distribution is described by mean va lue m, standard deviation σ

• 68% of values are within m ±σ • 95% of values are within m ±2σ Gaussian distribution used in planning margin calculations

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Slow Fading – Gaussian Distribution Normal / Gaussian Distributio n Standard Deviation, = 7 dB 0.07000

1 0.06000

2

2πσ

Normal / Gaussian Distribution 0.05000

0.04000

•d

0.03000

0.02000

0.01000

0.00000 -25

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-20

-15

-10

-5

0

5

10

15

20

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Fast Fading Different signal paths interfere and affect the received signal • Rice Fading – the dominant (usually LOS) path exist

• Rayleigh Fading – no dominant path exist

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Fast Fading – Rayleigh Distribution It can be theoretically shown that fast fading follows Rayleigh Distribution when there is no single dominant multipath component

• Applicable to fast fading in obstructed paths • Valid for signal level in linear scale (e.g. mW, W)

level (dB) +10 0 -10 -20 -30

0

1

2

3

4

5m

920 MHz v = 20 km/h 26


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Fast Fading – Rician Distribution Fast fading follows Rician distribution when there is a dominant multipath component, for example line-of-sight component combined with in-direct components

• Sliding transition between Gaussian and Rayleigh • “Rice-factor” K = r/A: direct / indirect signal energy  K=0 Rayleigh K >>1  Gaussian K=0 (Rayleigh) K=1 K=5

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Module Contents Reflections, Diffractions And Scattering Multipath And Fading Propagation Slope And Different Environments

• Free Space Loss • Received power with antenna gain • Propagation slope

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Free Space Loss Free space loss proportional to 1/d 2

• Simplified case: isotropic antenna • Which part of total radiated power is found within surface A? • Power density S = P/A = P / 4 πd 2  Received power within surface A : P = P/A * A • Received power reduces with square of distance ´

´

´

Surface A = 4π * d 2

A´´ = 16*A A´ = 4*A

d assume surface A´= 1m2

A d 2d 4d

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Received power with antenna gain

P s

Power density at the receiving end

S =

Effective receiver antenna area

λ 2 A eff = G R 4 π

Received power

P r = Aeff S

4π d 2

G s  λ  = G s Gr   P s  4π d 

P r

P s

P r

As

Ar

Gs

Gr

2

d

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04 RA41204EN20GLA0 Radio Propagation Fundamentals v03

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